Khujandī: Abū Maḥmūd Ḥāmid ibn al‐Khiḍr al‐Khujandī

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BornKhujand, (Tajikstan), circa945


Khujandī was an astronomer of some repute who constructed a variety of instruments and contributed to the mathematics supporting astronomical work. He is best known for the first very large mural quadrant that was intended to make solar observations of unprecedented accuracy. Only a few details are known of his life; he was likely one of the khans of Khujanda in Transoxania and was supported by the Būyid ruler Fakhr al‐Dawla.

Khujandī's towering achievement, the giant mural sextant near Rayy, was perhaps the most ambitious instrument of its time. Named al‐suds al‐Fakhrī (after its sponsor Fakhr al‐Dawla), it consisted of 60° of a meridian arc about 43 m in diameter, built at and below ground level. A small aperture in the roof of the building that housed the instrument allowed a cone of the Sun's rays to shine through. A circle with crosshatch lines was placed on the rays that fell onto the scale in order to determine their center. The scale w